Temperature compensated latching phase shifter having compensating dielectric in aperture of ferrite core

ABSTRACT

A ferrite core latching phase shifter uses the long remanent state as a reference state and thereby provides inherent temperature compensation of the reference phase. The temperature compensation is further augmented by placing in the aperture of the phase shifter a dielectric material selected to have an appropriate dielectric constant and temperature coefficient thereof, thereby providing a core comprised of a composite of the dielectric material and the ferrite. The addition of the dielectric material causes changes of the insertion phase attributable to thermally induced changes of the dielectric constant of the composite core, to offset changes of the insertion phase attributable to thermally induced changes of the remanent magnetization.

United States Patent 1 Smith [54] TEMPERATURE COMPENSATED LATCI-IING PHASE SHIFTER HAVING COMPENSATING DIELECTRIC IN APERTURE OF FERRITE CORE [75] Inventor: Peter W. Smith, Norwalk, Conn.

[73] Assignee: United Aircraft Corporation, East Hartford, Conn.

[22] Filed: Oct. 4, 1971 [21] Appl. No.: 185,974

52 U.S.Cl. ..333/24.1, 333/9811 51 Int. Cl. ..'..H0lp 1/32 58 Field ofSearch ..333/1.1,24.1,24.2,

[56] References Cited UNITED STATES PATENTS 3,316,506 Whicker et al. ..333/24.l

Jones et al ..333/24.-1

[ May 22, 1973 Primary ExaminerPaul L. Gensler Attorney-Melvin P. Williams ABSTRACT A ferrite core latching phase shifter uses the long remanent state as a reference state and thereby provides inherent temperature compensation of the reference phase. The temperature compensation is further augmented by placing in the aperture of the phase shifter a dielectric material selected to have an appropriate dielectric constant and temperature coefficient thereof, thereby providing a core comprised of a composite of the dielectric material and the ferrite. The addition of the dielectric material causes changes of the insertion phase attributable to thermally induced changes of the dielectric constant of the composite core, to offset changes of the insertion phase attributable -to thermally induced changes of the remanent magnetization.

1 Claim, 9 Drawing Figures Patented May 22, 1973 3,735,291

4 Sheets-$heet 1 Patented May 22, 1973 3,735,291

4 Sheets Sheet 4 1 TEMPERATURE COMPENSATED LATCHING PHASE SHIFTER HAVING COMPENSATING DIELECTRIC IN APERTURE OF FERRITE CORE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to micro-wave phase shifters and more particularly to latching phase shifters.

2. Description of the Prior Art In a phased array radar apparatus, a beam pointing angle of transmitted signals is determined by a phase shift (called an insertion phase, hereinafter) resulting from an appropriate delay of each of the signals transmitted by a multiplicity of antenna elements. An interference pattern of the signals causes the effective beam pointing angle and determines the level of side lobes of the signal transmission. Ferrite core devices, similar to wave guides and referred to as latching phase shifters, are commonly used to provide a variable insertion phase required for phased array radars and other microwave apparatus.

A latching phase shifter provides a quiescent insertion phase that is dependent upon the dielectric constant of its ferrite core and deviations from this quiescent insertion phase are proportional to the cores flux density. The ferrite core provides a highly desirable property in that the flux density caused by the introduction of a magnetic field remains substantially unchanged after the magnetic field is removed; this phenomenon is referred to as latching. Because the core latches, it is not usual to maintain the magnetic field after magnetization to a desired flux density. The flux density of the core, in the absence of a field, is hereinafter called remanent magnetization.

In a typical application, the core of the phase shifter is first saturated by a magnetic field having a strength more than sufficient to cause saturation, so that after removal of the field the phase shifter is latched in a reference state and provides a known insertion phase associated with the flux density caused by the saturation. A differential change of insertion phase, called a phase change hereinafter, is introduced by applying and removing a smaller field of opposite polarity, so that the phase shifter is latched in a remanent state associated with a flux density below the saturation level. The smaller field is selected to cause the phase shifter to latch in a desired remanent state associated with a desired insertion phase.

The magnetic field is induced in the phase shifter by applying a voltage pulse to a flux drive wire of one or more turns wound through an aperture in the core. The resulting change of flux density is proportional to the duration of the pulse. For applications such as a phased array radar apparatus, the voltage pulses applied to flux drive wires of a multiplicity of phase shifters are controlled by a computer; it causes the desired remanent state of the cores of the phase shifters to vary in a man- I with the reference state is referred to hereinafter as a difference between the reference phase and a desired insertion phase, is provided by causing the phase shifter to change from its reference state and latch in a desired remanent state. The reference phase, however, is highly temperature dependent and causes a similar temperature dependence of the insertion phase. In the phased array radar apparatus, local heating may cause unequal temperature of the phase shifters, thereby causing thermally dependent changes of insertion phase which generate errors in the beam pointing angle.

Phase shifters that have been constructed in accordance with the teachings of the prior art usually employ bulky heat sinks, are expensive, uncompensated for local heating and perform badly in an environment where temperature is variable.

SUMMARY OF THE INVENTION The object of the present invention is to provide a latching phase shifter having improved thermal stability charactistics.

According to the present invention, an aperture of a core of a latching phase shifter contains a material whose dielectric constant and temperature coefficient thereof is selected to compensate for temperature coefficients of the cores dielectric constant and remanent magnetization, thereby causing the reference phase of said phase shifter to be substantially independent to temperature.

In further accord with the present invention, strips of a first dielectric material having a dielectric constant with a positive temperature coefficient and strips of a second dielectric material having a dielectric constant with a negative coefficient are inserted in the aperture of the core, the relative amount of said first and second materials selected to compensate for temperature coefficients of the cores dielectric constant and remanent magnetization thereby causing the reference phase of said phase shifter to be substantially independent of temperature.

According to another aspect of the present invention, a latching phase shifter provides a desired insertion phase by first applying and removing a magnetic field that causes the core of said phase shifter to be in a major remanent state where the temperature coefficients of the remanent magnetism and dielectric constant of the core are offsetting in their effects upon a reference phase associated therewith, and thereafter applying a smaller selected magnetic field, causing the core to have a desired flux density associated with a desired insertion phase.

In further accord with the present invention, a latching phase shifter having a ferrite core provides a desired insertion phase by first applying and removing a magnetic field, causing the ferrite core to be in a long remanent state, and thereafter applying a smaller selected magnetic field, causing the ferrite core to have a desired flux density with a desired insertion phase.

The invention provides ferrite phase shifters having a reference insertion phase that is temperature stable over a wide temperature range.

Other objects, features and advantages of the present invention will become more apparent in the light of the following detailed description of preferred embodiments thereof as illustrated in the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an elevation side view of a preferred embodiment of the invention.

FIG. 2 is a section elevation view taken along line 22 of FIG. 1.

FIG. 3 is a curve of the insertion phase as a function of temperature of a phase shifter with a first hypothetical core.

FIG. 4 is a curve of the insertion phase as a function of temperature of a phase shifter with a second hypothetical core.

FIG. 5 is a curve of the insertion phase as a function of temperature of the phase shifter with a core consisting of a dielectric material.

FIG. 6 is a curve of the insertion phase as a function of temperature of a phase shifter with a ferrite core.

FIG. 7 is a curve of the insertion phase as a function of temperature of a phase shifter with a compensated ferrite core.

FIG. 8 is a magnetization curve of the ferrite core of latching phase shifter.

FIG. 9 is a perspective view of a strip of dielectric material.

DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention has two aspects which relate to the temperature compensation of a latching phase shifter. The first aspect is choosing as a reference state a major remanent state associated with a reference phase having a reduced temperature coefficient; the second is altering the dielectric constant of the core of the phase shifter to further reduce the temperature coefficient of the reference phase.

Referring now to FIGS. 1 and 2, a phase shifter common to both aspects of the present invention is comprised of a ferrite core 12 with a quarter wave matching transformer 14 at each end. The transformers 14 are well known in the art and consist of a low loss dielectric material, such as a suitable plastic, that is cemented to the ferrite core 12. An aperture 16 extends through the ferrite core 12, and a flux drive wire 18 located therein has its ends brought out through grooves 20 in the transformers 14. A voltage pulse source 24 is connected to the drive wire 18 and provides variable duration voltage pulses for changing the remanent state of the phase shifter. The input and output signal connections to the phase shifter may be made by any of a plethora of well known microwave devices which abut the free ends of the transformers 14.

For an understanding of the teachings of the invention a phase shifter is successively considered with each of two hypothetical cores, with an actual ferrite core 12, and lastly with an actual ferrite core 12 that has been altered to provide temperature compensation of the phase shifter.

A first hypothetical core has a zero temperature coefficient of its dielectric constant and a nonzero temperature coefficient of its remanent magnetism. Referring now to FIG. 3, the insertion phase as a function of temperature of the phase shifter with a first hypothetical core unmagnetized and in each of its major remanent states is shown by contours 26, 28, 30, respectively.

The unmagnetized core (contour 26) causes an insertion phase that is constant as a function of temperature because it behaves like a slab of dielectric material having an invariant dielectric constant. When magnetized in either major remanent state, the temperature coefficient of the insertion phase is associated with the temperature coefiicient of the remanent magnetization. The slopes of the contours 28, 30 are opposite because in either major remanent state, remanent magnetization decreases as the temperature of the core increases, thereby causing the contours 28, 30 to converge toward an insertion phase associated with less remanent magnetization.

A second hypothetical core has a zero temperature coefficient of its remanent magnetization and a nonzero temperature coefficient of its dielectric constant. Referring now to FIG. 4, the insertion phase as a function of temperature of the second hypothetical core in an unmagnetized state and in each of its major remanent states is shown by contours 32, 34, 36, respectively. The contours 32, 34, 36 are all parallel because in any given condition of magnetization, changes of the insertion phase as a function of temperature are only attributable to changes of the dielectric constant of the core.

An actual ferrite core, as is well known, is of a composite nature, having nonzero temperature coefficients associated with its remanent magnetization and its dielectric constant. In this embodiment, the ferrite core 12 has an insertion phase as a function of temperature that may be represented as a composite of FIG. 3 and FIG. 4 as is illustrated in FIG. 6. Contours 38, 40, 42 are composites of contours 26, 28, 30 (FIG. 3) and contours 32, 34, 36 (FIG. 4). It should be noted that the contour 40 is representative of a higher insertion phase but has a lower temperature coefficient than the lower insertion phase represented by the contour 42. The major remanent state associated with the contour 40 is a composite of contours 28 (FIG. 3) and 34 (FIG. 4) which have opposite slopes because of offsetting effects of the temperature coefficients of the remanent magnetization and dielectric constant of the core 12. The major remanent state associated with the contour 42 is a composite of contours 30 (FIG. 3) and 36 (FIG. 4) having slopes in the same direction because of additive effects of the temperature coefficients of the remanent magnetization and dielectric constant of the core 12. In accordance with the first aspect of the invention, a reduced temperature instability of the reference phase results from using as the reference phase the major remanent state associated with off-setting effects of the temperature coefficients of remanent magnetization and dielectric constant of the core 12.

In ferrite core phase shifters, the major remanent state which provides the larger insertion phase (contour 40) is known in the art as the long remanent state; the other major remanent state (contour 42) is known as a short remanent state. The long remanent state always provides a lower temperature coefficient of the insertion phase than the short remanent state because of the offsetting magnetic and dielectric effects explained hereinbefore. In further accord with the first aspect of the invention, the long remanent state is used as a reference state for the ferrite core latching phase shifter and provides less inherent temperature instability as clearly illustrated by the difference of the slopes of the contours 40, 42.

In accordance with the second aspect of the invention, the reference phase is made substantially independent of temperature by altering the dielectric properties of the core 12 so that the effects of the temperature coefficients of the remanent magnetization (FIG. 3) and the dielectric constant (FIG. 4) substantially offset each other. Referring to FIG. 5, a phase shifter having a core consisting of a dielectric material provides an insertion phase represented by the contour 43; the temperature coefficient of the insertion phase is opposite from the temperature coefficient of the insertion phase associated with the second hypothetical core. Addition of the dielectric material to the aperture of the second hypothetical core causes contours of the insertion phase which are a composite of the contour 43 and the contours 32, 34, 36 (FIG. 4). The contours 44, 46, 48 are representative of how the contours 32, 34, 36 are changed by altering the dielectric properties of the core 12, as hereinbefore described.

Referring now to FIG. 7 a contour 49 is an illustration of the reference phase as a function of temperature after the dielectric properties of the core 12 have been altered so that the contour 28 (FIG. 3) and the contour 46 (FIG. 4) form a composite with substantially completely offsetting temperature characteristics. A con tour 50 illustrates a modified temperature coefficient of the insertion phase associated with the short remanent state.

A composite core, having dielectric properties different from those of the ferrite core 12, is formed by a dielectric material homogeneously mixed with an inert liquid adhesive, the resulting mixture being placed in the aperture 16; the mixture hardens and adheres to the inside of the core 12. In one specific embodiment of the invention, a phase shifter comprised of a core 12 made of magnesium manganese ferrite has a dielectric constant of 14.5 with a positive temperature coefficient of 580 parts/million/C in the Ku microwave band. A dielectric material, comprised of powdered barium titanate mixed with an inert powdered plastic filler and having a dielectric constant of 16 with a negative temperature coefficient of 740 parts/million/(I, is placed in the aperture 16 to achieve substantially complete temperature compensation.

It should be understood that variations of structure may cause the temperature coefficient of a cores remanent magnetization to be a greater factor than the temperature coefficient of its dielectric constant in causing the reference phase to vary as a function of temperature. Structures of this type require a dielectric material having a dielectric constant with a positive temperature coefficient for temperature compensation, in contrast with the specific embodiment described hereinbefore.

In another embodiment of the invention, a plurality of rectangular strips of two different dielectric materials are inserted into the aperture 16. A portion of the strips have a dielectric constant with a positive temperature coefficient and the remainder have a dielectric constant with a negative temperature coefficient. Referring to FIG. 9, the length of a strip 64 is substantially equal to the length of the core 12 so that upon insertion of the strip 64 into the core 12, the composite dielectric constant, and the temperature coefficient associated therewith, remains constant along the entire length of the core 12. Temperature stabilization of the phase shifter is provided by selecting the proportion of the different strips so that a modified dielectric constant with an appropriate temperature coefficient is obtained.

A desired insertion phase is achieved by providing the core 12 with a suitable dielectric material, magnetizing the core 12 to its reference state and then causing a change to a desired remanent state. Referring now to- FIG. 8, a saturation flux drive voltage pulse causes a current which magnetizes the core 12 to a flux density and field strength represented by a point 52. After the saturation flux drive voltage pulse ends, the core 12 latches in the long remanent state (used as a reference state) represented by the point 54. The reference phase obtained thereby is represented by the contour 49 (FIG. 7). A phase change to a desired insertion phase, represented by a contour 56 (FIG. 7), is obtained by applying a flux drive voltage pulse which causes a current which magnetizes the core 12 to a flux density and field strength represented by a point 58. After the flux drive voltage pulse ends, the core 12 latches in a desired remanent state represented by the point 60 which is associated with the desired insertion phase.

It should be noted that a vertical displacement between the contours 49, 50 represents maximum phase changes from the reference phase that may be provided by the phase shifter; the phase changes are about an order of magnitude less than the reference phase. Since the contours 48, 50 converge as temperature increases (at the Curie temperature, as is know in the art, far in excess of the temperatures illustrated in FIG. 7), a point where the contours 48, 50 meet is representative of the temperature above which no phase change is available.

Although the invention has been shown and described with respect to a preferred embodiment thereof, it should be understood by those skilled in the art that various changes and omissions in the form and detail thereof may be made therein without departing from the spirit and the scope of the invention.

Having thus described typical embodiments of my invention, that which I claim as new and desire to secure by Letters Patent of the United States is:

l. A temperature compensated latching waveguide phase shifter adapted for connection in series with microwave energy conduction means comprising:

a ferrite core in said waveguide having an aperture therein, said ferrite core having dielectric properties and magnetic properties with respect to which said core may be latched in a short remnant state or a long remnant state to provide an insertion phase to microwave energy passing therethrough, the insertion phase of said core as a function of said dielectric properties having a positive temperature coefficient, the insertion phase of said core as a function of said magnetic properties having a negative temperature coefficient when in the long remnant state and having a positive temperature coefficient when in the short remnant state;

a flux drive winding extending through said aperture and adapted for connection with a flux drive voltage source to provide an insertion phase of a selected one of said states; and

an insert of dielectric material disposed in the aperture of said core, said dielectric material having a temperature coefficient of effect on insertion phase which is opposite and substantially equal to the net temperature coefficient of effect on insertion phase of said core when in said selected one of said states, including the dielectric and magnetic temperature effects, so as to substantially compensate therefor and provide an insertion phase with substantially no temperature coefficient.

=l= t l 

1. A temperature compensated latching waveguide phase shifter adapted for connection in series with microwave energy conduction means comprising: a ferrite core in said waveguide having an aperture therein, said ferrite core having dielectric properties and magnetic properties with respect to which said core may be latched in a short remnant state or a long remnant state to provide an insertion phase to microwave energy passing therethrough, the insertion phase of said core as a function of said dielectric properties having a positive temperature coefficient, the insertion phase of said core as a function of said magnetic properties having a negative temperature coefficient when in the long remnant state and having a positive temperature coefficient when in the short remnant state; a flux drive winding extending through said aperture and adapted for connection with a flux drive voltage source to provide an insertion phase of a selected one of said states; and an insert of dielectric material disposed in the aperture of said core, said dielectric material having a temperature coefficient of effect on insertion phase which is opposite and substantially equal to the net temperature coefficient of effect on insertion phase of said core when in said selected one of said states, including the dielectric and magnetic temperature effects, so as to substantially compensate therefor and provide an insertion phase with substantially no temperature coefficient. 